The invention relates to an optical element suitable for separating and converting directions of polarization, comprising polarization-separating members arranged in a row extending transversely to an optical principal axis of the optical element for separating incident light from a light source into transmissive light having a first linear direction of polarization and reflective light having a second linear direction of polarization which is orthogonal to the first direction of polarization on a side facing the light source, said polarization-separating members having faces extending at an angle to the optical principal axis, and each polarization-separating member having a thickness in the direction of the optical principal axis and a width in a direction transverse to the optical principal axis, the optical element being further provided with polarization-converting members located on a side of the polarization-separating members remote from the light source for converting the first or the second direction of polarization into the second or the first direction of polarization.
The invention also relates to a projection system.
In such an optical element, which is known from United States patent U.S. Pat. No. 5,764,412, the optical axes, extending parallel to the optical principal axis, of the incident light of juxtaposed polarization-separating members are spaced regularly far apart. Spaced apart from the optical principal axis, a polarization-separating member is located on both sides of this axis, which member has a width of twice the width of the other polarization-separating members so as to ensure that, on a side remote from the light source, the optical axes of the exiting light of the polarization-separating members are spaced equally far apart as the optical axes of the incident light.
A drawback of the known optical element is that it is only suitable for separating and converting incident light beams extending parallel along the optical axes, which light beams are juxtaposed at regular distances, so that it is not suitable for applications in which the light beams are spaced apart at different distances.
It is an object of the invention to provide an optical element in which the drawbacks of the known optical element are obviated.
In the optical element according to the invention, this object is achieved in that polarization-separating members located proximate to the optical principal axis have a different width than polarization-separating members spaced apart from the optical principal axis, the optical axes of the polarization-separating members located proximate to the optical principal axis being located at a different distance from each other than the optical axes of the polarization-separating members spaced apart from the optical principal axis.
The width of the polarization-separating members is adapted to the desired mutual distance between the optical axes of the incident light beams. In this way, the optical element is suitable for use in, inter alia, an LCD projector which is provided with a light source, a light modulation panel and two interpositioned integrator plates, in which the light beams coming from the light source and exiting from the integrator plates are spaced apart at different distances.
An embodiment of the optical element according to the invention is characterized in that the polarization-separating members located proximate to the optical principal axis have a larger width than the polarization-separating members spaced apart from the optical principal axis.
Such an optical element is suitable for use in, inter alia, the above-mentioned LCD projector, in which the entering light beams on a side remote from the optical principal axis are located closer together than those proximate to the optical principal axis.
A further embodiment of the optical element according to the invention is characterized in that polarization-separating members located proximate to the optical principal axis have a larger thickness than polarization-separating members spaced apart from the optical principal axis.
Since the thickness of each polarization-separating member, desired at a given width, can thus be determined, a minimum quantity of optical material is sufficient to manufacture the optical element.
Another embodiment of the optical element according to the invention is characterized in that all polarization-separating members have the same thickness.
Both the side facing the light source and the side remote from the light source can then be easily processed to form a plane surface.
Yet another embodiment of the optical element according to the invention is characterized in that all polarization-separating members are co-planar on a side facing the light source.
Such an optical element can easily be secured to, for example, an integrator plate located between the light source and the optical element.
A further embodiment of the optical element according to the invention is characterized in that the polarization-separating members located on both sides of the optical principal axis extend alongside each on faces intersecting each other on a side remote from the light source.
In this way, the reflecting light passing through a polarization-separating member is incident on a member having the same or a larger width and/or thickness.
These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.